Liquid and dried maize root mucilage jointly regulate wettability during rhizosphere rewetting

Root mucilage can persist in the rhizosphere as dried coatings on soil particles after drying and can be remobilized as liquid mucilage upon rewetting. Although root mucilage plays a key role in regulating water dynamics at the root–soil interface, the coupled effects of these dried mucilage coatings and remobilized liquid mucilage on rhizosphere wettability during rewetting remain poorly understood. Here, we investigated how liquid and dried maize root mucilage jointly regulate wettability by measuring dynamic surface tension, water–n-decane interfacial tension, contact angles of probe liquids on dried mucilage-coated model surfaces, and the corresponding liquid and solid surface free energy components. Wetting envelopes were constructed, and an empirical two-factor model was developed to describe static contact angle as a function of liquid mucilage concentration and dried mucilage loading. Liquid maize root mucilage reduced both surface tension and interfacial tension in a concentration- and time-dependent manner, mainly by decreasing the polar component of the liquid surface energy from approximately 28.5 to 4.6 mN m⁻¹ as liquid mucilage concentration increased from 2 to 10 mg mL⁻¹. In contrast, increasing dried mucilage loading from 10 to 154 μg cm⁻² increased the water contact angle from about 41° to 120° and reduced the polar component of the solid surface energy from approximately 21.5 to 1 mN m⁻¹, indicating the formation of a low-polarity, water-repellent coating. The wetting envelopes and empirical model showed that dried and liquid mucilage exert opposite but coupled effects on wettability: dried mucilage enhances water repellency, whereas liquid mucilage partly restores wetting by modifying the surface energy of the invading liquid. These results suggest that mucilage-controlled rhizosphere wettability could be viewed as a dynamic liquid–solid process governed by both dried mucilage loading and liquid mucilage concentration, rather than by a fixed contact angle or liquid surface tension alone.